Ultrasonic anomalies in nickel and cobalt under static stress

Abstract

Using a pulse method, the attenuation of longitudinal ultrasonic waves is measured in nickel and cobalt under different static stresses up to 17 kg wt mm-2. The measurements are carried out at 20 and 90 °C for the ultrasonic frequencies 2, 3 and 6 MHz in magnetized and nonmagnetized specimens. Attenuation peaks are recorded at certain intermediate stresses independent of the frequency used. However, the position and height of the peaks are found to change with magnetization and temperature variation. This indicates a temperature-sensitive magnetic origin for the peaks observed. An explanation for the origin of such anomalies could be found in the rotation of the direction of spontaneous magnetization inside a magnetic domain, as a result of the applied stress. This view is supported by a calculation of the values of stress at which the attenuation peaks should appear; the calculated and experimental values of stress are found to be in good agreement